Field of the Invention
The present invention relates to the field of gas turbine engines, such as a jet engine or a turboprop engine for an airplane, and more specifically to a sealing device for a turbine of such an engine.
Description of the Related Art
A twin-body engine having a front fan, for example, comprises, from upstream to downstream, a fan, a low-pressure compressor, a high-pressure compressor, a combustor, a high-pressure turbine and a low-pressure turbine.
By convention, in the present application, the terms “upstream” and “downstream” are defined with respect to the direction of the flow of air in the jet engine. Similarly, by convention in the present application, the terms “interior” and “exterior”, “inferior” and “posterior”, and “inner” and “outer” are defined radially with respect to the axis of the engine. Thus, a cylinder which extends along the axis of the engine comprises an interior face, oriented toward the axis of the engine, and an exterior surface, oriented away from the interior surface of the cylinder.
A turbine of a gas turbine engine comprises several stages, each having a bladed rotor and a stator. Each rotor comprises a disk which bears, at its outer periphery, substantially radial blades, with the disks of the various wheels being connected coaxially to one another and to the drive shaft of the rotor of the turbine by appropriate means. Every stator comprises an inner annular platform and an outer annular platform, between which extend substantially radial vanes. The outer platform of the stator comprises means for latching and fastening onto an outer casing of the turbine.
The inner platform comprises a wall extending in the radial direction and an annular annulus connected to the wall. The wall and the annular annulus thus delimit an upstream cavity and a downstream cavity between the turbine stator and the turbine rotor. The annulus, the radial wall and the inner platform of the stator are generally formed of sectors, each having a single casting.
In use, the stator vanes are exposed to the hot gases flowing in the turbine duct. The temperature of the gases in the duct is relatively high, typically of the order of 900 degrees Celsius, whereas the temperature in the region between the inner platform of the stator and the rotor is lower, for example approximately 700 degrees Celsius.
In order to consolidate this temperature difference, a known turbine rotor comprises an upstream spur and a downstream spur, each defining a sealing baffle in, respectively, the upstream cavity and the downstream cavity delimited by the wall and the annular annulus so as to form a seal of the baffle effect type. The use of such spurs does not, however, make it possible to achieve sufficient fluidtightness given that the flow of gas can still pass through the sealing baffles formed upstream and downstream between the stator and the rotor. In particular, air recirculation vortices or eddies form and enter the cavities.
Moreover, a known annular annulus for a stator of a turbomachine further comprises, radially on its outer portion, one or more annular elements made of abradable material, designed to engage with outer annular lamellar elements, known as lips, of an element of the rotor, arranged radially so as to form a labyrinth seal. Such a seal makes it possible to direct the flow of air passing axially through the annular space located between the inner periphery of the stator and the rotor of the turbine. Thus, when the turbine rotor is in rotation, the lips of the labyrinth seal are driven in rotation while maintaining as little clearance as possible with respect to the abradable elements which remain stationary.
However, positioning the abradable elements in this way at the outer portion of the annular annulus, in a manner which extends the wall, means that their thermal inertia is considerable. This, in combination with the lower temperature to which they are exposed, acts counter to the thermal expansion of the stator vanes which are then subjected to substantial mechanical stresses. This can result in cracks appearing in these vanes, the life of which is shortened considerably.